Page 17 - Offshore Well Construction

CHAPTER 13
Advances in Technology
Petroleum Extension-The University of Texas at Austin

HORIZONTAL DRILLING
Horizontal drilling has become commonplace during the last decade and now covers the range of well types noted
below. In general, horizontal wells are drilled in development areas where the formations and pressures are known.
However, there is an extra time element required to plan and design a horizontal well—it will probably take twice as
long to plan, design, and order the equipment items, and take approximately 50% extra time to drill. This is due to the
additional cost of specialized equipment, safety constraints, and time taken to achieve the build along the horizontal
leg. Also, the longer the horizontal section that needs to be drilled, the lower the build rate. The majority of horizontal
wells are drilled using medium radius builds.

Additional factors need to be considered when drilling a horizontal well, especially the need for primary well control
where there is a greater requirement to maintain constant bottomhole pressure during a well kill. Hole cleaning is also
more difficult due to the presence of ‘dune buildup’ across the build sections, and can also increase the chances of
swabbing. Horizontal drilling has become the norm in many areas where the requirement is to maximize production.
The current distance records are hampered only by the equipment limits of the respective drilling rigs, especially the
hoisting capacity and maximum flow rates and pump capacity.

Definition
Horizontal drilling is the process of directing a drill bit to follow a horizontal path, approximately 90 degrees from
vertical.

Purposes

Maximize production
Enhance secondary production
Enhance ultimate recovery
Reduce the number of wells required to develop a field

Main Types
Short radius (1°–4°/1 ft) shallow wells, can go from vertical—horizontal in 50 ft
Medium (8°–20°/100 ft) fractured reservoirs, need 300 ft to achieve build
Long radius (2°–8°/100 ft) offshore, inaccessible reservoirs, need 1,500 ft
Ultra short radius (almost no build)

Applications
Tight reservoirs (permeability < 1 md)
Fractured reservoirs
Economically inaccessible reservoirs
Heavy oil reservoirs
Channel sand and reef core reservoirs
Reservoirs with water/gas coning problems
Stratified thin reservoirs

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